In existing simulcast systems, an address of a selective call receiver is transmitted at a low data rate (e.g., 512 or 1200 bits per seconds) by a plurality of base sites. A response from a selective call receiver with acknowledge-back capability is used by a central site (a control site which co-ordinates the plurality of base sites) to determine the proximity of the selective call receiver with respect to the base site or base sites that received the acknowledgement. The central site directs a message at a substantially higher data rate (e.g., 2400 or 4800 bits per second or higher data rates as required) to the base site nearest to the selective call receiver, which broadcasts the message to the selective call receiver. Because the message is broadcasted in a non-simulcast mode, the message data rate can be substantially higher than the data rate used when simulcasting the addresses.
Generally, in any selective call receiver system, the goal is to reduce wasted air time, thus making it more cost effective to consumers who subscribe to this system. Simulcasting the address at a low data rate and sending the message at a higher data rate will generally reduce the air time particularly when transmitting long messages. Additionally, there are cases when it is more economical to have more than one "high" message data rate for different messages. For example, a long message or the particular location of the selective call receiver with respect to a base site may make necessary to have more than one "high" message rate. However, increasing the number of message rates will significantly increase the cost of the transmitters and receivers in the base sites. More importantly, increasing the number of message rates used to transmit different messages will significantly increase the cost of selective call receivers, because it will be desirable or necessary to have the selective call receivers capable of receiving all the available message rates for the different messages. The additional cost of such a selective call receiver may be less attractive to many subscribers.